Polymer for a glass ionomer cement

ABSTRACT

A process for producing a water-soluble, hydrolysis-stable, polymerizable polymer, comprising a) a step of copolymerizing a mixture comprising (i) a first copolymerizable monomer comprising at least one optionally protected carboxylic acid group and a first polymerizable organic moiety, and (ii) a second copolymerizable monomer comprising one or more optionally protected primary and/or secondary amino groups and a second polymerizable organic moiety, for obtaining an amino group containing copolymer; b) a step of coupling to the amino group containing copolymer a compound having a polymerizable moiety and a functional group reactive with an amino group of repeating units derived from the second copolymerizable monomer in the amino group containing copolymer obtained in the first step wherein the optionally protected amino group is deprotected, so that polymerizable pendant groups are linked to the backbone by hydrolysis-stable linking groups, and, optionally, a step of deprotecting the protected carboxylic acid group after step (a) or step (b), for obtaining a polymerizable polymer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of the U.S. patentapplication Ser. No. 13/988,049, currently pending, which is a nationalstage application of PCT/EP2011/006446, filed on Dec. 20, 2011, whichclaims the benefit of and priority to EP Application Ser. No.10015981.3, filed on Dec. 22, 2010, which is herein incorporated byreference for all purposes.

FIELD OF THE INVENTION

The present invention relates to a process for the production of awater-soluble, hydrolysis-stable and polymerizable polymer for a glassionomer cement. Moreover, the present invention relates to an polymerfor a glass ionomer cement, which is obtainable by the process of thepresent invention and a dental composition comprising the polymer for aglass ionomer cement. Furthermore, the present invention relates to theuse of the polymer for the preparation of a dental composition, inparticular a dental cement.

According to the process of the present invention, it is possible toconveniently and efficiently obtain a hydrolysis-stable andpolymerizable polymer for a glass ionomer cement at a high molecularweight, which is resistant to acidic media and capable of furthercrosslinking providing improved storage stability and long-termmechanical resistance of a dental ionomer cement.

BACKGROUND OF THE INVENTION

WO03011232 discloses resin-modified glass ionomer cements containing apolymer having a plurality of acidic repeating units and a plurality ofpolymerizable vinyl groups which can be formed in one method bypartially reacting a material such as a polymeric acid anhydride with amonomer containing an acid- or acid anhydride-reactive group andcontaining one or more vinyl groups that will provide the desiredpolymerizable functionality. The acid- or acid anhydride-reactive groupreacts with acid units or anhydride units in a the polymeric precursorto provide pendant vinyl groups in the resulting reaction product sothat a hydrolyzable polymer is obtained. Another method involvescopolymerizing anα, β-unsaturated carboxylic acid and a suitableα,β-unsaturated monomer containing one or more such pendant vinyl groups,whereby a crosslinked product cannot be avoided.

WO03061606 discloses ionomeric cements containing a polymerizableionomer which is obtainable based on three carboxylic acid monomers, twoof which are acrylic acid and itaconic acid, and the third monomer is anacryloyl- or methacryloyl derivative of an amino acid, wherebypolymerizable pendant groups are not linked to the backbone byhydrolysis-stable linking groups.

Dental restorative materials are known for restoring the function,morphology and integrity of dental structures damaged by physical damageor caries-related decay of enamel and/or dentin. Dental restorativematerials can be divided into two classes, indirect restorativematerials and direct restorative materials.

Indirect restorations such as inlays, onlays, crowns or bridges areadhered to the damaged residual hard dental tissue with a specificdental composition, such as a dental resin cement. Adequate adhesion ofthe restoration typically requires the application of a primer as apre-treatment step.

Direct restorative materials, such as dental composites are applieddirectly onto the dental surface and subsequently cured in situ.However, direct restorations often require pre-treatment with anadhesive or primer to enhance adhesive strength.

Common to all dental restorations is that they require highbiocompatibility, resistance to the severe conditions present in theoral cavity, particularly over a longer period of time.

Glass ionomer cements (GIC), which are cured by an acid-base reactionbetween silicate glass powder and a polyalkenoic acid, provide highbiocompatibility, good direct adhesion to the dental hard tissues andcariostatic properties through the release of fluoride ions and arewidely used as direct dental restorative materials.

However, conventional glass ionomer cements are relatively brittle dueto low flexural strength properties. The resistance of glass ionomercements to mechanical stress may be improved by the choice of thepolymer for a glass ionomer cement. For example, a polymer for a glassionomer cement, which has polymerizable moieties as pendant groups canbe crosslinked to increase the mechanical resistance of the resultingglass ionomer cement.

Moreover, for the purpose of the cement reaction as well as forproviding adhesive properties of the dental composition to hard dentaltissue, acidic groups in the polymer are required. However, acidicgroups accelerate hydrolysis of pendant functional groups linked to thepolymer backbone by hydrolysable groups such as ester groups. Thus, apolymer to be used in a dental composition desirably has a plurality ofcarboxylic acid groups and at the same time a high stability with regardto hydrolysis in order to avoid degradation of the composition duringstorage or when applied to hard dental tissue.

Japanese Patent Publication No. 2005-65902A discloses a dental adhesivecomposition comprising, as a polymerizable monomer containing aparticular carboxylic acid, a carboxylic acid compound having a(meth)acryloyl group and a carboxyl group which are bound to an aromaticgroup. However, such a polymerizable monomer having an ester groupquickly degrades in an acidic medium.

Chen et al. and Nesterova et al. (Chen et al., J. Appl. Polym. Sci., 109(2008) 2802-2807; Nesterova et al., Russian Journal of AppliedChemistry, 82 (2009) 618-621) disclose copolymers of N-vinylformamidewith acrylic acid and/or methacrylic acid, respectively. However, noneof these documents mentions the introduction of a further polymerizablemoiety into the copolymer.

WO2003/011232 discloses water-based medical and dental cements that canbe post-polymerized after the cement reaction. The dental cementsconsist of two separate polymers, wherein one of the polymers has apendant post-polymerizable moiety linked to the polymer through an esterbond. However, this ester bond between the polymer and the polymerizablemoieties is again prone to hydrolytic cleavage in acidic media.Moreover, crosslinking of the glass ionomer may lead to the shrinkage ofthe dental composition in particular when the molecular weight of thecrosslinking polymer is low.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process forpreparing a polymer for a dental composition, wherein the polymer hasgood adhesive strength to dental hard tissue, high stability againsthydrolysis in an acidic medium and wherein the polymer may becrosslinked during curing for improving the mechanical resistance of thedental cement, and whereby shrinkage stress during polymerization of thedental composition during crosslinking is reduced or even avoidedwhereby the problem of shrinkage of the dental composition during curingis alleviated.

The present invention provides a process for producing a water-soluble,hydrolysis-stable, polymerizable polymer, comprising

-   -   a) a step of copolymerizing a mixture comprising        -   (i) a first copolymerizable monomer comprising at least one            optionally protected carboxylic acid group and a first            polymerizable organic moiety, and        -   (ii) a second copolymerizable monomer comprising one or more            optionally protected primary and/or secondary amino groups            and a second polymerizable organic moiety,        -   for obtaining an amino group containing copolymer;    -   b) a step of coupling to the amino group containing copolymer a        compound having a polymerizable moiety and a functional group        reactive with an amino group of repeating units derived from the        second copolymerizable monomer in the amino group containing        copolymer obtained in the first step wherein the optionally        protected amino group is deprotected,        and, optionally, a step of deprotecting the protected carboxylic        acid group after step (a) or step (b), for obtaining a        polymerizable polymer.

Specifically, in the step of coupling to the amino group containingcopolymer a compound having a polymerizable moiety and a functionalgroup reactive with an amino group of repeating units derived from thesecond copolymerizable monomer in the amino group containing copolymerobtained in the first step, the polymerizable pendant groups are linkedto the backbone by hydrolysis-stable linking groups. The linkagepreferably does not contain an ester group.

Moreover, the present invention provides a polymer obtainable by theprocess as defined above.

Furthermore, the present invention provides a dental compositioncomprising the polymer as defined above.

Finally, the present invention provides a use of a polymer as definedabove for the preparation of a dental composition.

The process of the present invention provides a polymer useful in aglass ionomer cement, which is hydrolysis-stable and can be polymerizedto yield a dental glass ionomer cement of improved mechanicalresistance. The polymer may be provided with a high amount of acidicgroups resulting in an excellent adhesion to dental hard tissue.Moreover, since the process of the present invention provides a polymerhaving a high molecular weight, any polymer shrinkage during the curingreaction may be easily controlled.

The present inventors have recognized that resin reinforced dental glassionomer cements are subject to deterioration during storage or aftercuring in the mouth of the patient. The present inventors have furtherrecognized that the deterioration is due to hydrolytic degradation ofthe resin component conventionally containing hydrolyzable moieties. Thepresent inventors have then recognized that by using a specific processfor the preparation of a polymer, an improved water-soluble,hydrolysis-stable, polymerizable polymer may be prepared at a highmolecular weight which overcomes the drawbacks of conventional resinreinforced glass ionomer cements known from the prior art. Inparticular, the present invention is based on the recognition that theintroduction of amino group containing repeating units into the backboneof the polymer opens up the possibility to provide high molecular weightcopolymers which may be easily and efficiently functionalized by theintroduction of polymerizable pendant groups linked to the backbone byhydrolysis stable linking groups so that the disadvantages ofconventional polymerizable resin components may be avoided. Based on theunique and unexpected effect of the orientation of the amino carbonylgroup present in the polymer of the present invention in relation to thepolymer backbone and the pendant groups, the present invention wasaccomplished.

According to the present invention, a two-step process is requiredwherein the step of forming an amino group containing copolymer byaddition polymerizing a monomer mixture is separate from a step ofintroducing polymerizing pendant groups in a polymer analog reaction inorder to avoid crosslinking of the polymer backbone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The process for the preparation of a water-soluble, hydrolysis-stable,polymerizable polymer according to the present invention comprises forobtaining a polymerizable polymer a step a) and a step b), andoptionally a step c).

Generally, a polymer for a glass ionomer cement is an organic polymericcompound comprising ionizable pendant groups, such as carboxylic acidgroups. The carboxylic acid groups of a polymer can react with asuitable glass component to form a glass ionomer cement which can beused as a dental material.

A “polymerizable polymer for a glass ionomer cement” according to thepresent invention is a polymer containing one or more polymerizablemoieties allowing polymerization and crosslinking of the polymer afterthe formation of a glass ionomer cement, increasing the long-termmechanical resistance of the material.

Herein, “water-soluble” means that at least 0.1 g, preferably 0.5 g ofthe polymer dissolves in 100 g of water at 20° C.

“Hydrolysis-stable” means that the polymer is stable to hydrolysis in anacidic medium, such as in a dental composition. Specifically, thepolymer does not contain groups such as ester groups which hydrolyze inaqueous media at pH3 at room temperature within one month.

Step a) of the process of the present invention is a step ofcopolymerizing a mixture comprising a first copolymerizable monomercomprising at least one optionally protected carboxylic acid group and afirst polymerizable organic moiety and a second copolymerizable monomercomprising one or more optionally protected primary and/or secondaryamino groups and a second polymerizable organic moiety for obtaining anamino group containing copolymer. The mixture may also contain furthermonomers.

The first copolymerizable monomer to be used in step a) comprises atleast one, preferably one to three, more preferably one or two, mostpreferably one optionally protected carboxylic acid group(s).

The protecting group of an optionally protected carboxylic acid group isnot particularly limited as long as it is a carboxyl-protecting groupknown to those of ordinary skill in the art of organic chemistry (cf. P.G. M. Wuts and T. W. Greene, Greene's Protective Groups in OrganicSynthesis, 4th Edition, John Wiley and Sons Inc., 2007). Preferably, thecarboxyl-protecting group is selected from a trialkylsilyl group, analkyl group and an arylalkyl group. More preferably, thecarboxyl-protecting group is selected from an alkyl group or anarylalkyl group. Most preferably, the carboxyl-protecting group isselected from a tert-butyl group and a benzyl group. In one preferredembodiment, the carboxyl-protecting group is a tert-butyl group.

A polymerizable organic moiety is an organic moiety of a molecule whichcan be used to covalently link this molecule in a chemical reaction(polymerization) to other molecules reactive with this moiety to form amacromolecule of repeating or alternating structural units. Preferably,this polymerizable organic moiety is a carbon-carbon double bond as inthe case of an ethylenically unsaturated moiety.

In a preferred embodiment of the process of the present invention, thefirst copolymerizable monomer is represented by the general formula (1):

In formula (1), R¹ is a hydrogen atom, a —COOZ group or a straight chainor branched C₁₋₆ alkyl group which may be substituted by a —COOZ group.Preferably, R¹ is a hydrogen atom, a —COOZ group or a methyl group. Morepreferably, R¹ is a hydrogen atom or a methyl group.

In formula (1), R² is a hydrogen atom, a —COOZ group or a straight-chainor branched C₁₋₆ alkyl group which may be substituted by a —COOZ group.Preferably, R² is a hydrogen atom or a —COOZ group. More preferably, R²is a hydrogen atom. In formula (1), the dotted line indicates that R²may be in either the cis or trans orientation.

In formula (1), A is a single bond or a straight-chain or branched C₁₋₆alkylene group which group may contain 1 to 3 heteroatoms in between twocarbon atoms of the alkylene carbon chain, which heteroatoms areselected from an oxygen atom, nitrogen atom, and sulfur atom, and/orwhich alkylene group may contain in between two carbon atoms of thealkylene carbon chain 1 to 3 groups selected from an amide bond or aurethane bond. Preferably, A is a single bond or a straight-chain orbranched C₁₋₆ alkylene group which group may contain a heteroatom inbetween two carbon atoms of the alkylene carbon chain, which heteroatomis selected from an oxygen atom or a nitrogen atom, and/or whichalkylene group may contain in between two carbon atoms of the alkylenecarbon chain a group selected from an amide bond or a urethane bond.More preferably, A is a single bond or a straight-chain C₁₋₆ alkylenegroup. Most preferably, A is a single bond.

In formula (1), Z which may be the same or different independentlyrepresents a hydrogen atom, a metal ion, a protecting group for acarboxylic acid group, or the Z forms with a further —COOZ group presentin the molecule an intramolecular anhydride group. The metal ion may bea monovalent metal ion such as an alkali metal ion. In one embodiment, Zis a protecting group for a carboxylic acid group. In anotherembodiment, Z is a hydrogen atom.

When Z forms with a further —COOZ group present in the molecule anintramolecular anhydride group (—C(O)OC(O)—), the further —COOZ groupmay be preferably present on R¹ such as in case of itaconic acidanhydride.

In a preferred embodiment, Z is a hydrogen atom and the polymerizationreaction is conducted in an alkaline environment. In an alternativepreferred embodiment, Z is a hydrogen atom and the amino groups of thefirst copolymerizable monomer and of the second copolymerizable monomercarry a protecting group.

Preferably, a first copolymerizable monomer is a protected (meth)acrylicacid monomer. More preferably, a first polymerizable monomer is selectedfrom tert-butyl acrylate and benzyl acrylate. Most preferably, a firstpolymerizable monomer is tert-butyl acrylate.

In a preferred embodiment of the process of the present invention, thesecond copolymerizable monomer is represented by the general formula(2):

In formula (2), R³ is a hydrogen atom or a straight chain or branchedC₁₋₆ alkyl group which may be substituted by a —COOZ′ group. Preferably,R³ is a hydrogen atom. In formula (2), the dotted line indicates that R³may be in either the cis or trans orientation.

In formula (2), X is a protected amino group or a hydrocarbon grouphaving 1 to 20 carbon atoms, which is substituted with an amino groupwhich may carry a protecting group, wherein the hydrocarbon group maycontain 1 to 6 heteroatoms, which heteroatoms are selected from anoxygen atom, nitrogen atom, and sulfur atom, and/or which hydrocarbongroup may contain a group selected from an amide bond or a urethane bondand which hydrocarbon group may further be substituted with up to 6groups selected from —COOZ′, amino groups, hydroxyl groups and thiolgroups. Preferably, X is a hydrocarbon group having 1 to 20 carbonatoms, which is substituted with an amino group which may carry aprotecting group, wherein the hydrocarbon group may contain aheteroatom, which heteroatom is selected from an oxygen atom and anitrogen atom, and/or which hydrocarbon group may contain a groupselected from an amide bond or a urethane bond and which hydrocarbongroup may further be substituted with a —COOZ′ group. More preferably, Xis a hydrocarbon group having 1 to 20 carbon atoms, even more preferably1 to 6 carbon atoms, which is substituted with an amino group which maycarry a protecting group, wherein the hydrocarbon group may contain anoxygen atom and/or which hydrocarbon group may contain an amide bond andwhich hydrocarbon group may further be substituted with a —COOZ′ group.In as specific embodiment wherein X is a protected amino group, thecompound of formula (2) is allyl amine, wherein the amino group carriesa protecting group.

The protecting group of a protected amino group or an optionallyprotected amino group is not particularly limited and may be anyconventional protecting group for an amino group as, for example,described in P. G. M. Wuts and T. W. Greene, Greene's Protective Groupsin Organic Synthesis, 4th Edition, John Wiley and Sons Inc., 2007.Preferably, the amino-protecting group is selected from an acyl group,an arylalkyl group, an alkoxy carbonyl group, and an aryloxycarbonylgroup. More preferably, the amino-protecting group is an acyl group.Most preferably, the amino-protecting group is a formyl group.

In formula (2), Y is a hydrogen atom or a hydrocarbon group having 1 to20 carbon atoms, wherein the hydrocarbon group may contain 1 to 6heteroatoms, which heteroatoms are selected from an oxygen atom,nitrogen atom, and sulfur atom, and/or which hydrocarbon group maycontain a group selected from an amide bond or a urethane bond and whichhydrocarbon group may further be substituted with up to 6 groupsselected from —COOZ′, amino groups, hydroxyl groups and thiol groups.Preferably, Y is a hydrogen atom or a hydrocarbon group having 1 to 20carbon atoms, wherein the hydrocarbon group may contain a heteroatom,which heteroatom is selected from an oxygen atom and a nitrogen atom,and/or which hydrocarbon group may contain a group selected from anamide bond or a urethane bond and which hydrocarbon group may further besubstituted with a —COOZ′ group. More preferably, Y is a hydrogen atomor a hydrocarbon group having 1 to 20 carbon atoms, even more preferably1 to 6 carbon atoms, wherein the hydrocarbon group may contain an oxygenatom and/or which hydrocarbon group may contain an amide bond and whichhydrocarbon group may further be substituted with a —COOZ′ group. In onepreferred embodiment, Y is a hydrogen atom.

In formula (2), Z′ which may be the same or different, independentlyrepresents a hydrogen atom, a metal ion, a protecting group for acarboxylic acid group, or the Z′ forms with a further —COOZ′ grouppresent in the molecule an intramolecular anhydride group. In oneembodiment, Z′ is a protecting group for a carboxylic acid group. Inanother embodiment, Z′ is a hydrogen atom. The metal ion may be amonovalent metal ion such as an alkali metal ion. In another embodiment,Z′ is a hydrogen atom. When Z forms with a further —COOZ′ group presentin the molecule an intramolecular anhydride group (—C(O)OC(O)—).

In a preferred embodiment, Z′ is a hydrogen atom and the polymerizationreaction is conducted in an alkaline environment. In an alternativepreferred embodiment, Z′ is a hydrogen atom and the amino groups of thesecond copolymerizable monomer carry a protecting group.

In one embodiment, the second copolymerizable monomer comprises a secondcopolymerizable organic moiety selected from the group of(meth)acrylamide moieties which may be substituted and substituted(meth)acrylic acid which may be protected. In another embodiment, thesecond copolymerizable monomer is selected from allyl amine, aminopropylvinyl ether, aminoethyl vinyl ether, N-vinyl formamide and 2-aminomethylacrylic acid. In a preferred embodiment, the second copolymerizablemonomer is aminopropyl vinyl ether. The amino group may be in the formof an ammonium salt such as a ammonium chloride. Preferred structuresare as follows wherein the amino group may also carry a protectinggroup:

The molar ratio of first copolymerizable monomer and secondcopolymerizable monomer in the mixture copolymerized in step (a) (molfirst copolymerizable monomer/mol second copolymerizable monomer) is inthe range of from 100:5 to 5:100, preferably in the range from 50:5 to5:20, more preferably in the range from 40:5 to 1:1.

The further copolymerizable monomers optionally to be used in step a)comprise at least one, preferably one to three, more preferably one ortwo, most preferably one optionally protected acidic group(s) which arenot carboxylic acid groups. Specific examples of acidic groups aresulfonic acid groups (—SO₃M), phosphonic acid groups (—PO₃M₂) orphosphoric acid ester groups (—OPO₃M.₂), or salts thereof, wherein M mayindependently be a hydrogen atom or a monovalent ion such as an alkalimetal or an ammonium ion.

Specific examples of the optional further monomers are selected from2-Acrylamido-2-methylpropane sulfonic acid, vinyl phosphonate, and vinylsulfonic acid.

In a preferred embodiment, the solutions containing the firstcopolymerizable monomer and the second copolymerizable monomer areseparately saturated with nitrogen before combining them forcopolymerization to minimize possible side-products of a competitiveAza-Michael addition.

Step a) of the process of the present invention proceeds as achain-growth polymerization. In one embodiment, step a) comprisesradical copolymerization.

The type of copolymer formed by step a) of the present invention may bea statistical copolymer, a random copolymer, an alternating copolymer, ablock copolymer or a combination thereof.

A copolymer obtained by step a) of the present invention is an aminogroup containing copolymer, such as, for example, a copolymer obtainableby copolymerization of acrylate and aminopropyl vinyl ether.

The reaction conditions of the polymerization reaction according to stepa) of the present invention are not particularly limited. Accordingly,it is possible to carry out the reaction in the presence or absence of asolvent. A suitable solvent may be selected from the group of water,dimethyl formamide (DMF), tetrahydrofurane (THF), and dioxane.

The reaction temperature is not particularly limited. Preferably, thereaction is carried out at a temperature of between −10° C. to theboiling point of the solvent. Preferably, the reaction temperature is inthe range of from 0° C. to 80° C.

The reaction time is not particularly limited. Preferably the reactiontime is in the range of from 10 minutes to 48 hours, more preferably 1hour to 36 hours.

The reaction is preferably carried out in the presence of apolymerization initiator. In a preferred embodiment of the process ofthe present invention, the polymerization initiator is selected fromazobisisobutyronitrile (AIBN),2,2-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis(2-methylbutyronitrile),2,2′-azobis(N,N′-dimethyleneisobutyramidine) dihydrochloride, and4,4′-azobis(4-cyano pentanoic acid). The amount of the polymerizationinitiator is not particularly limited. Suitably, the amount is in therange of from 0.001 to 5 mol % based on the total amount of themonomers.

The reaction product obtained in step a) may be isolated byprecipitation and filtration. The product may be purified by washingwith a suitable solvent.

Step b) of the process of the present invention is a step of coupling acompound having a polymerizable moiety and a functional group reactivewith an amino group of repeating units derived from the secondcopolymerizable monomer in the amino group containing copolymer obtainedin the first step wherein the optionally protected amino group isdeprotected.

Preferably, the coupling reaction in step (b) is an addition reaction ora condensation reaction forming a bond selected from an amide bond, aurea bond or a thiourea bond.

By a functional group reactive with an amino group, herein is meant anygroup which can form a covalent bond with an amino group of the aminogroup containing copolymer. Preferably, a functional group reactive withan amino group is a carboxylic acid group or a derivative thereof suchas an ester group or an anhydride thereof, an isocyanate group or anisothiocyanate group. More preferably, a functional group reactive withan amino group is a carboxylic acid group or a derivative thereof.

If the amino group of repeating units derived from the secondcopolymerizable monomer in the amino group containing copolymer obtainedin the first step is protected, the amino group can be deprotected priorto step (b) or concomitant with step (b).

The conditions for deprotection of an optionally protected amino grouphave to be selected according to the protecting group used. Preferably,the protected amino group is deprotected by hydrogenolysis or treatmentwith acid or base.

If the deprotection of a protected amino group is carried outconcomitantly with step (b), it will be understood by a person skilledin the art that the deprotection conditions and the conditions for step(b) have to be selected so that both reactions can proceed efficiently.

In a preferred embodiment of the process of the present invention, thecompound having a polymerizable moiety and a functional group reactivewith an amino group of repeating units derived from the secondcopolymerizable monomer is a compound of formula (3):

In formula (3), R⁴ is a hydrogen atom or a straight chain or branchedC₁₋₆ alkyl group which may be substituted by a —COOZ group and R⁵ is ahydrogen atom or a straight-chain or branched C₁₋₆ alkyl group which maybe substituted by a —COOZ group. Preferably, R⁴ is a hydrogen atom andR⁵ is a hydrogen atom or a methyl group. More preferably, R⁴ is ahydrogen atom and R⁵ is a methyl group. In formula (3), the dotted lineindicates that R⁴ may be in either the cis or trans orientation.

In formula (3), Z″ which may be same or different, independentlyrepresents a hydrogen atom, a metal ion, a protecting group for acarboxylic acid group, or the Z″ forms with a further —COOZ″ grouppresent in the molecule an intramolecular anhydride group.

In one embodiment, Z″ is a protecting group for a carboxylic acid group.In another embodiment, Z″ is a hydrogen atom. In a preferred embodiment,Z is a hydrogen atom and the polymerization reaction is conducted in analkaline environment. In an alternative preferred embodiment, Z″s ahydrogen atom and the amino groups of the second copolymerizable monomercarry a protecting group.

In one embodiment, in formula (3), LG is a leaving group. Preferably, LGis a chlorine atom or a bromine atom, or forms with the adjacentcarbonyl group a carboxylic acid anhydride moiety. Preferably, LG is agroup which is suitable for reacting the compound of formula (3) in aSchotten-Baumann type reaction.

In another embodiment, LG may replace Z and form with R⁴ or R⁵ anintramolecular carboxylic acid anhydride group.

In yet another embodiment two molecules of formula (3) form anintermolecular carboxylic acid anhydride group by sharing a common LG,wherein LG is an oxygen atom.

Preferably, the compound having a polymerizable moiety and a functionalgroup reactive with an amino group of repeating units derived from thesecond copolymerizable monomer forms a carboxylic acid anhydride group.More preferably, the compound forms an intermolecular carboxylicanhydride group with a second compound of formula (3). Most preferably,the compound forms (meth)acrylic anhydride.

The coupling according to step b) of the present invention serves tointroduce one or more polymerizable moieties into the amino groupcontaining copolymer, which moieties can be post-polymerized to provideadditional covalent crosslinking, imparting additional strength to thedental material comprising the copolymer.

In one embodiment of the process of the present invention, thecarboxylic acid groups of the copolymer obtained in step b) are notprotected and the copolymer can be used as a polymer according to thepresent invention without further treatment. In an alternativeembodiment, the carboxylic acid groups of the copolymer obtained in stepb) are protected and the carboxylic acid groups have to be deprotectedbefore the copolymer exhibits the features of a polymer according to thepresent invention.

The reaction conditions of the reaction according to step b) of thepresent invention are not particularly limited. Accordingly, it ispossible to carry out the reaction in the presence or absence of asolvent. A suitable solvent may be selected from the group of dimethylformamide (DMF), tetrahydrofurane (THF), and dioxane.

The reaction temperature is not particularly limited. Preferably, thereaction is carried out at a temperature of between −10° C. to theboiling point of the solvent. Preferably, the reaction temperature is inthe range of from 0° C. to 80° C.

The reaction time is not particularly limited. Preferably the reactiontime is in the range of from 10 minutes to 48 hours, more preferably 1hour to 36 hours.

The reaction of step (a) s is preferably carried out in the presence ofa polymerization initiator. In a preferred embodiment of the process ofthe present invention, the polymerization initiator is selected fromazobisisobutyronitrile (AIBN),2,2-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis(2-methylbutyronitrile),2,2′-azobis(N,N′-dimethyleneisobutyramidine) dihydrochloride, and4,4′-azobis(4-cyano pentanoic acid). The amount of the polymerizationinitiator is not particularly limited. Suitably, the amount is in therange of from 0.001 to 5 mol % based on the total amount of themonomers.

The reaction product obtained in step b) may be isolated byprecipitation and filtration. The product may be purified by washingwith a suitable solvent.

The process of the present invention optionally includes a step ofdeprotecting the protected carboxylic acid group after step (a) or step(b), for obtaining a polymerizable polymer. In a preferred embodiment,the process of the present invention includes a step of deprotecting theprotected carboxylic acid group for obtaining a polymerizable polymer.In a further preferred embodiment, the process of the present inventionincludes a step of deprotecting the protected carboxylic acid groupafter step (b).

The conditions for deprotection of an optionally protected carboxylgroup are selected according to the protecting group used. Preferably,the protected carboxyl group is deprotected by hydrogenolysis ortreatment with acid or base.

A first embodiment of the process of the present invention isillustrated by the following scheme wherein a amino group protectedvinyl amine is reacted with acrylic acid for obtaining a polymerbackbone having a protected amino group. The copolymer is preferably arandom copolymer. In a further step, the protected amino groups of thepolymer backbone are liberated and coupled to a polymerizable groupcontaining moiety, whereby a polymer of the invention is obtained havingacidic groups reactive in a cement reaction wherein ionic bonds areformed, and having polymerizable groups reactive in a crosslinkingreaction wherein covalent bonds are formed.

In the above scheme, any acrylamide group may be replaced by amethacrylamide group A second embodiment of the process of the presentinvention is illustrated by the following scheme wherein protectedacrylic acid is reacted with an amino group containing polymerizablevinyl ether derivative for obtaining an amino group containing polymerbackbone. In a further step, the amino groups of the polymer backboneare couples to a polymerizable group containing moiety. Finally, thecarboxylic acid groups are liberated whereby a polymer of the inventionis obtained having acidic groups reactive in a cement reaction whereinionic bonds are formed, and having polymerizable groups reactive in acrosslinking reaction wherein covalent bonds are formed.

In the above scheme, any acrylamide group may be replaced by amethacrylamide group

According to the present invention a novel polymer is provided. Thepolymer of the invention may be exemplified by the following preferredstructures.

In the above structures, the numbers refer to the number of additionalcarbon atoms introduced by each of the side chain as compared to acorresponding polyacrylic acid. Since a polymer having (a+b) repeatingunits contains b times the number of additional carbon atoms in additionto the number of carbon atoms in a polyacrylic acid having (a+b)carboxylic acid groups, but b times less carboxylic acid groups, thewater solubility may be reduced. On the other hand, the introduction ofan additional ionic group such as a —COOH group is capable ofcompensating the decrease in water solubility, and is also indicatedabove. Preferably, the number of side chains b, the number of additionalcarbon atoms and the number of additional carboxylic acid groups areadjusted so as to provide a useful water solubility of the polymer ofthe present invention.

Accordingly, in a preferred embodiment, the side chains of the polymerwhich are linked to the polymer backbone via an amide bond, urea bond orthio urea bond contain one or more additional acidic groups, preferablycarboxylic acid groups.

A polymerizable polymer according to the present invention, which isobtainable by the process as described above, is particularly useful forglass-ionomer cement (GIC) systems. A polymer according to the presentinvention preferably has an average molecular weight M_(w) in the rangeof from 1,000, in particular 10,000 to 1,000,000 Da. More preferably,the average molecular weight M_(w) is in the range of from 100,000 to700,000 Da, or 50,000 to 250,000 Da.

The formation of such a cement, which is useful as a dental material, isbased on a reaction between a reactive particulate filler, such as apowdered metal oxide or hydroxide, mineral silicate, or ion leachableglass or ceramic, and an ionic polymer, e.g. a polyalkenoic acid.Preferably, such a glass-ionomer cement is formed by reacting a polymeraccording to the present invention with a fluoroaluminosilicate glass(FAS glass).

Polymers to be used in such a system must be sufficient in number orpercent by weight of carboxylic acid groups to bring about the settingor curing reaction in the presence of the modified particulate reactiveand/or non-reactive filler.

A dental composition according to the present invention, comprises thepolymer as described above and may additionally contain a particulatereactive and/or non-reactive filler, an initiator system, one or moreadditional comonomers.

Examples of reactive particulate filler materials include materialscommonly known in the art of dental compositions such as calcium orstrontium-containing and aluminum-containing materials. Preferably,particulate reactive fillers contain leachable fluoride ions. Specificexamples of particulate reactive fillers are selected from calciumalumino silicate glass, calcium alumino fluorosilicate glass, calciumaluminumfluoroborosilicate glass, strontium aluminosilicate glass,strontium aluminofluorosilicate glass, strontiumaluminofluoroborosilicate glass. Suitable particulate reactive fillersfurther include metal oxides such as zinc oxide and magnesium oxide, andion-leachable glasses, e.g., as described in U.S. Pat. Nos. 3,655,605,3,814,717, 4,143,018, 4,209,434, 4,360,605 and 4,376,835.

Suitable non-reactive fillers may be selected from fillers currentlyused in dental restorative compositions.

The filler may have a unimodal or polymodal (e.g., bimodal) particlesize distribution. The filler can be an inorganic material. It can alsobe a crosslinked organic material that is insoluble in the polymerizableresin, and is optionally filled with inorganic filler. The filler can beradiopaque, radiolucent or non-radiopaque. Examples of suitablenon-reactive inorganic fillers are naturally-occurring or syntheticmaterials such as quartz, nitrides such as silicon nitride, glassesderived from, for example Ce, Sb, Sn, Zr, Sr, Ba and Al, colloidalsilica, feldspar, borosilicate glass, kaolin, talc, titania, and zincglass, and submicron silica particles such as pyrogenic silicas.Examples of suitable non-reactive organic filler particles includefilled or unfilled pulverized polycarbonates or polyepoxides. Preferablythe surface of the filler particles is treated with a coupling agent inorder to enhance the bond between the filler and the matrix. The use ofsuitable coupling agents includesgamma-methacryloxypropyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,and the like.

The particulate filler usually has an average particle size of from0.005 to 100 μm, preferably of from 0.01 to 40 μm as measured, forexample, by electron microscopy or by using a conventional laserdiffraction particle sizing method as embodied by a MALVERN MastersizerS or MALVERN Mastersizer 2000 apparatus. The particulate filler may be amultimodal particulate reactive filler representing a mixture of two ormore particulate fractions having different average particle sizes. Theparticulate reactive filler may also be a mixture of particles ofdifferent chemical composition. In particular, it is possible to use amixture of a particulate reactive material and a particulatenon-reactive material. The particulate reactive filler may be surfacemodified by a surface modifying agent.

As an initiator, any compound or system, capable of initiating thecopolymerization reaction according to the present invention may besuitably used. The initiator may be based on a radical initiator and maybe a photoinitiaor or a redox initiator or a mixture thereof. A suitablephotoinitiator may comprise camphor quinone/amine, ortrimethylbenzoyl-diphenyl-phosphine oxide (TPO). A suitable redoxinitiator may be selected from benzoyl peroxide/amine, potassiumperoxodisulfate (K₂S₂O₈)/ascorbinic acid, sodium peroxodisulfate, sodiumpyrosulfite (Na₂S₂O₅)

A suitable comonomers contain at least one polymerizable functionalgroup. Suitable polymerizable functional groups are ethylenicallyunsaturated groups (e. g. alkenyl groups and preferably vinyl groups).Preferred examples are substituted and unsubstituted acrylates,methacrylates, or alkenes.

A dental composition according to the present invention may also includea modifying agent such as tartaric acid, for adjusting the working timeand a setting time of the glass ionomer cement reaction, respectively,when preparing the cement as described in U.S. Pat. Nos. 4,089,830,4,209,434, 4,317,681 and 4,374,936. In general, an increase in workingtime results in an increase in setting time as well.

The “working time” is the time between the beginning of the settingreaction when the polymer and modified particulate reactive filler arecombined in the presence of water, and the time the setting reactionproceeds to the point when it is no longer practical to perform furtherphysical work upon the system, e.g. spatulate it or reshape it, for itsintended dental or medical application.

The “setting time” is the time measured from the beginning of thesetting reaction in a restoration to the time sufficient hardening hasoccurred to allow subsequent clinical or surgical procedures to beperformed on the surface of the restoration.

In a setting reaction, due to the presence of polymerizable doublebonds, a polymerization reaction takes place.

A dental composition according to the present invention may furthercontain solvents, pigments, nonvitreous fillers, free radicalscavengers, polymerization inhibitors, bisacrylamides such asN,N′-diethyl-1,3-bisacrylamido-propan (BADEP), 1,3-bisacrylamido-propan(BAP), and 1,3-bisacrylamido-2-ethyl-propan (BAPEN), reactive andnonreactive diluents e.g., 2-hydroxyethyl methacrylate (HEMA),hydroxypropyl methacrylate, surfactants (such as to enhance solubilityof an inhibitor e. g., polyoxyethylene), coupling agents to enhancereactivity of fillers e.g., 3-(trimethoxysilyl) propyl methacrylate, andrheology modifiers.

Suitable solvents or nonreactive diluents include alcohols such asethanol and propanol. Suitable reactive diluents are alpha,betaunsaturated monomers for providing altered properties such as toughness,adhesion, and set time.

Suitable alpha,beta-unsaturated monomers may be acrylates andmethacrylates such as methyl acrylate, methyl methacrylate, ethylacrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate,isopropyl acrylate, isopropyl methacrylate, 2-hydroxyethyl acrylate,2-hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate,hydroxypropyl methacrylate, tetrahydrofurfuryl acrylate,tetrahydrofurfuryl methacrylate, glycidyl acrylate, glycidylmethacrylate, the diglycidyl methacrylate of bis-phenol A (“bis-GMA”),glycerol mono- and di-acrylate, glycerol mono- and di-methacrylate,ethyleneglycol diacrylate, ethyleneglycol dimethacrylate,polyethyleneglycol diacrylate (where the number of repeating ethyleneoxide units vary from 2 to 30), polyethyleneglycol dimethacrylate (wherethe number of repeating ethylene oxide units vary from 2 to 30especially triethylene glycol dimethacrylate (“TEGDMA”), neopentylglycol diacrylate, neopentylglycol dimethacrylate, trimethylolpropanetriacrylate, trimethylol propane trimethacrylate, mono-, di-, tri-, andtetra-acrylates and methacrylates of pentaerythritol anddipentaerythritol, 1,3-butanediol diacrylate, 1,3-butanedioldimethacrylate, 1,4-butanedioldiacrylate, 1,4-butanediol dimethacrylate,1,6-hexane diol diacrylate, 1,6-hexanediol dimethacrylate,di-2-methacryloyloxethyl hexamethylene dicarbamate,di-2-methacryloyloxyethyl trimethylhexanethylene dicarbamate,di-2-methacryloyl oxyethyl dimethylbenzene dicarbamate,methylene-bis-2-methacryloxyethyl-4-cyclohexyl carbamate,di-2-methacryloxyethyl-dimethylcyclohexane dicarbamate,methylene-bis-2-methacryloxyethyl-4-cyclohexyl carbamate,di-1-methyl-2-methacryloxyethyl-trimethyl-hexamethylene dicarbamate,di-1-methyl-2-methacryloxyethyl-dimethylbenzene dicarbamate,di-1-methyl-2-methacryloxyethyl-dimethylcyctohexane dicarbamate,methylene-bis-1-methyl-2-methacryloxyethyl-4-cyclohexyl carbamate,di-1-chloromethyl-2-methacryloxyethyl-hexamethylene dicarbamate,di-1-chloromethyl-2-methacryloxyethyl-trimethylhexamethylenedicarbamate, di-1-chloromethyl-2-methacryloxyethyl-dimethylbenzenedicarbamate, di-1-chloromethyl-2-methacryloxyethyl-dimethylcyclohexanedicarbamate, methylene-bis-2-methacryloxyethyl-4-cyclohexyl carbamate,di-1-methyl-2-methacryloxyethyl-hexamethylene dicarbamate,di-1-methyl-2-methacryloxyethyl-trimethylhexamethylene dicarbamate,di-1-methyl-2-methacryloxyethyl-dimethylbenzene dicarbamate,di-1-methyl-2-metha-cryloxyethyl-dimethylcyclohexane dicarbamate,methylene-bis-1-methyl-2-methacryloxyethyl-4-cyclohexyl carbamate,di-1-chloromethyl-2-methacryloxyethyl-hexamethylene dicarbamate,di-1-chloromethyl-2-methacryloxyethyl-trimethylhexamethylenedicarbamate, di-1-chloromethyl-2-methacryloxyethyl-dimethylbenzenedicarbamate, di-1-chloromethyl-2-methacryloxyethyl-dimethylcyclohexanedicarbamate,methylene-bis-1-chloromethyl-2-methacryloxyethyl4-cyclohexyl carbamate,2,2′-bis(4-methacryloxyphenyl)propane, 2,2′bis(4-acryloxyphenyl)propane,2,2′-bis[4(2-hydroxy-3-methacryloxy-phenyl)]propane,2,2′-bis[4(2-hydroxy-3-acryloxy-phenyl)propane,2,2′-bis(4-methacryloxyethoxyphenyl)propane,2,2′-bis(4-acryloxyethoxyphenyl)propane,2,2′-bis(4-methacryloxypropoxyphenyl)propane,2,2′-bis(4-acryloxypropoxyphenyl)propane,2,2′-bis(4-methacryloxydiethoxyphenyl)propane,2,2′-bis(4-acryloxydiethoxyphenyl)propane,2,2′-bis[3(4-phenoxy)-2-hydroxypropane-1-methacrylate]propane, and2,2′-bis[3(4-phenoxy)-2-hydroxypropane-1-acryalte]propane, may bementioned. Other suitable examples of polymerizable components areisopropenyl oxazoline, vinyl azalactone, vinyl pyrrolidone, styrene,divinylbenzene, urethane acrylates or methacrylates, epoxy acrylates ormethacrylates and polyol acrylates or methacrylates. Mixtures ofalpha,beta-unsaturated monomers can be added if desired. Preferably, themixed but unset dental compositions of the invention will contain acombined weight of about 0.5 to about 40%, more preferably about 1 toabout 30%, and most preferably about 5 to 20% water, solvents, diluentsand alpha,beta-unsaturated monomers, based on the total weight(including such water, solvents, diluents and alpha,beta-unsaturatedmonomers) of the mixed but unset dental composition components.

An example of a suitable free radical scavenger is 4-methoxyphenol. Anexample of a suitable inhibitor is tert.-butyl hydroquinone (TBHQ),hydroxytoluene or butylated hydroxytoluene (BHT). The amount ofinhibitor may be selected from 0.001 to 2% and preferably from 0.02 to0.5% based on the total weight of the copolymer/comonomer/water mixture.

A polymer according to the present invention may be used for thepreparation of a dental composition. The dental composition may be adental material to be used in the oral cavity. Dental compositionsaccording to the present invention are useful as restorative and fillingmaterials, luting cements, adhesive cements, base or orthodonticcements, cavity liners and bases, pit and fissure sealants.

The invention will now be further illustrated by the following Examples.

EXAMPLES Example 1 1. Copolymerisation of tert.-Butylacrylat (tButA) and3-Aminopropylvinylether (APVE) to poly(tButA-co-APVE)

5.0 g (39 mmol) tButA, 0.99 g (9.8 mmol, 20 mol-%) APVE and 0.16 g (2mol-%) AIBN were separately dissolved in DMF and the solutions weresaturated with N₂. Then the solutions were combined and stirred for 24 hat 70° C. After the polymerization the cooled solution was diluted withDMF to 30 wt-% polymer solutions and precipitated in water/methanol(9:1). The separated solid was dried in vacuum.

The obtained copolymer had a molecular weight M_(n)=18 kDa, an M_(w)=51kDa and a PD of 2.8.

IR-spectroscopy of the product showed no vinylether-vibrations while¹H-NMR showed broadened peaks for the aliphatic protons and no peaks forpossible remaining double bond protons.

¹H-NMR (500 MHz, DMSO-d₆): δ (ppm)=3.5 (2H,4), 2.7 (2H, 6), 2.2 (2H, 2),1.8 (1H, 1), 1.6 (2H, 5), 1.44 (9H, 3).

2. Methacrylation of the poly(tButA-co-APVE)

To a solution of 5 g (33.7 mmol) copolymer poly(tButA-co-APVE) dissolvedin 31.5 g dichloromethane were added 1.3 g (8.42 mmol) methacrylic acidanhydride. After stirring the solution for 24 h at ambient temperature,the solvent was removed and the crude product was dissolved in 30 mLmethanol. From this solution the polymer was precipitated in water,filtered off and dried in vacuum.

FT-IR: ν_(max) [cm⁻¹]=2976, 2932, 1785, 1722 (Ester), 1670 (Amid I),1626 (C═C), 1526 (Amid II), 1479, 1448, 1392, 1366, 1143, 844.

3. Hydrolysis of Ester Moieties

To a solution of 1.0 g (8.15 mmol) of the methacrylatedpoly(tButA-co-APVE) in 5 mL chloroform were added 20 wt-% trifluoroacetic acid. After stirring the solution for 5 h at 60° C. the crudeprecipitated polymer was separated from the solvent. The polymer waswashed with chloroform, dissolved in methanol and re-precipitated inchloroform. Then the yellow polymer was dried in vacuum.

¹H-NMR (500 MHz, DMSO-d₆): δ (ppm)=12.2 (1H, —COOH), 7.8 (1H, —NH—), 5.6(1H, —C═C—H), 5.3 (1H, C═C—H), 2.2 (2H, —CH₂-backbone), 1.8 (3H, —CH₃),1.8 (1H, —CH—, backbone), 1.5 (2H, O—CH₂CH₂), 1.4 (9H, C—(CH₃)₃,residual ester moieties).

Example 2 1. Copolymerization of tert butyl acrylate (t-BA) and3-aminopropyl vinylether (APVE) to poly(AA-co-APVE)

In a three necked round bottom flask, equipped with a cooler, 2.34 mL(0.0206 mol) APVE and 8.97 mL (0.0618 mol) t-BA were mixed with 20 mLdioxane. 278 mg AIBN (2 mol-% regarding the total monomers) weredissolved, too. The reaction mixture was instantaneously flushed withArgon for about 20 min. Meanwhile a metal bath was preheated to 90° C.The polymerization was instantaneously started by placing the bath belowthe flask. After 1 h of stirring the reaction was complete. A sample of5 mL was withdrawn and diluted with dioxane to 20 mL. The polymer wasprecipitated by adding this solution to an excess of 150 mL water. Thepolymer was dried at the vacuum pump. The molecular weight wasdetermined by using SEC with DMF as eluent.

M_(n)=11500 g/mol, M_(w)=38100 g/mol, PD=3.32

2. Modification of poly(AA-co-APVE) with Methacrylic Anhydride

To the residue of the reaction mixture from synthetic step 1 cooled downto room temperature were added 26 mg tert.-butyl hydroquinone (TBHQ) todeactivate the residual initiator. Than 0.0309 mol methacrylic anhydridewere added. After stirring the mixture for 2 h at room temperature, thesolvent was removed at the rotary evaporator (30° C.) and afterwards thesample was dried at the vacuum pump. The NMR-spectra shows broadenedpeaks at 5.30 ppm and 5.64 ppm of double bonds indicating that themodification was successful.

3. Hydrolysis of tert.-butyl Ester Moieties

20 g of a polymer with 5 mol-% APVE incorporated were modified withmethacrylic anhydride as described above. After removing the solvents atthe rotary evaporator the crude product was dissolved in 50 mL oftrifluoroacetic acid. The mixture was cooled in an ice bath which wasslowly dissolving and stirred for 24 h. Over night the polymerprecipitated. The suspension was decanted and the polymer was dissolvedin 100 mL of dioxane. It was precipitated in a fivefold excess ofacetone. The precipitate was dissolved again in dioxane and precipitatedagain. Afterwards the polymer was first dried at the rotary evaporatorand afterwards at the vacuum pump. The NMR-spectra shows that the peakof the tert-butyl group at 1.38 ppm has nearly vanished. Thiscorresponds to a degree of hydrolysis of 98 mol-%.

Example 3 Copolymerisation of tert.-butylacrylate and3-aminopropylvinylether-P(tBu-co-APVE)

A solution of 15 g (117 mmol) tert.-Butylacrylat in 38 g DMF wassaturated under ice cooling with nitrogen. 3 g (29 mmol)3-Amino-propylvinylether were added to this solution after 15 minutes.Further 5 minutes later were added 480 mg (2 mol-%) AIBN in nitrogencounter flow. Then the solution was stirred for 24 h at 70° C. After thepolymerization the cooled solution was diluted with DMF to 33 wt-%polymer solutions and precipitated in the 20-fold quantity of water. Thesolid was filtered off, washed with water and dried in vacuum.

FT-IR: ν_(max) [cm⁻¹]=2977 (—CH₂—), 1723 (ester), 1481, 1449, 1392,1366, 1255, 1144, 845.

¹H-NMR (500 MHz, CDCl₃): δ(ppm)=3.5 (2H, —O—CH₂—), 2.7 (2H, —CH₂—NH₂),2.2 (2H, backbone), 1.8 (1H, backbone), 1.6 (2H, —O—CH₂—CH₂—), 1.44 (9H,-tbutyl).

GPC (DMF): M_(n)=26 kDa, M_(w)=70 kDa, M_(z)=124 kDa, PD=2.7.

The following table shows typical molecular masses for differentpolymerization samples using a ratio of eq(tBA):eq(APVE)=3:1:

c(AIBN) t_(term.) Batch # [mol-%] [min.] M_(n) M_(w) M_(z) PD 044-020 410 35.600 81.000 137.000 2.3 30 40.000 64.200 94.000 1.6 60 40.40060.700 85.100 1.5 1440 36.000 65.200 97.300 1.8 044-022 1 10 14.90037.400 72.900 1.9 30 14.800 39.200 71.700 1.8 60 150.800 160.200 166.4001.0 044-023 0.1 30 69.700 106.900 146.400 1.5

Itaconic Amide Modified P(tBA-co-APVE-IA)

To a clear solution of 3.0 g p(tBA-co-APVE) in 10 mL dichloro methanewere added portion wise under stirring 0.4 g (3.6 mmol) itaconic acidanhydride, whereby the solution discolorates red and then yellowish.Then the solution was stirred for 24 h at room temperature prior toevaporate dichloro methane.

FT-IR: ν_(max) [cm⁻¹]=2977 (—CH₂—), 1718 (ester), 1668 (amide I), 1559(amide II), 1476, 1437, 1392, 1367, 1252, 1146, 1100, 945, 843.

Hydrolysis of Ester Moieties to P(AA-co-APVE-IA)

The modified polymer was added portion wise under stirring to 10 mLtrifluoro acetic acid, and stirred some hours at room temperature priorto evaporate the trifluoro acetic acid in vacuum. The obtained highviscous polymer was dissolved in water and dialyzed for 4 days(MWCO=1000 g/mol). After frieze drying a reddish solid was received.

FT-IR: ν_(max) [cm⁻¹]=3392, 2932 (—CH₂—), 1699 (acid), 1625 (—C═C), 1546(amide II), 1447, 1407, 1230, 1164, 1094, 934, 798, 610

¹H-NMR (300 MHz, D₂O): δ (ppm)=8.0 (1H, —NH—), 6.4 (1H, —C═C—H), 5.6(1H, —C═C—H), 3.5 (2H, —O—CH₂—), 3.4 (2H, —NH—CH₂—), 3.3 (2H,—NH—CO—CH₂), 2.4 (1H, backbone), 2.0-1.5 (2H, backbone), 1.6 (2H,—O—CH₂—CH₂—).

Example 4 Methacrylamide Modified P(tBA-co-APVE-MA)

To a clear solution of 3.0 g p(tBA-co-APVE) of example 4 dissolved in 10mL dichloro methane were added drop wise 0.6 g (4.1 mmol) methacrylicacid anhydride.

Then the solution was stirred for 24 h at room temperature prior toevaporate dichloro methane. The obtained raw product was applied forfurther reactions without purification.

FT-IR: □_(max) [cm⁻¹]=3351, 2977 (—CH₂—), 1721 (ester), 1668 (amide I),1622 (—C═C), 1531 (amide II), 1452, 1392, 1366, 1255, 1146, 1089, 940,845.

Hydrolysis of Ester Moieties to P(AA-co-APVE-MA)

The modified polymer was added portion wise under stirring to 10 mLtrifluoro acetic acid, and stirred some hours at room temperature priorto evaporate the trifluoro acetic acid in vacuum. The obtained highviscous polymer was dissolved in water and dialyzed for 4 days(MWCO=1000 g/mol). After frieze drying a colorless solid was received.

FT-IR: ν_(max) [cm⁻¹]=3180, 2934 (—CH₂—), 2613, 1701 (acid), 1650 (amideI), 1597, 1537 (amide II), 1449, 1408, 1211, 1162, 1110, 919, 797, 611

¹H-NMR (300 MHz, D₂O): δ (ppm)=8.0 (1H, —NH—); 5.7 (1H, —C═C—H), 5.4(1H, —C═C—H), 3.5 (2H, —O—CH₂—), 3.5 (2H, —NH—CH₂—), 2.2 (1H, backbone),1.8-1.6 (2H, backbone), 1.6 (2H, —O—CH₂—CH₂—).

Example 5 Acrylamide Modified P(tBA-co-APVE-AA)

To a solution of 5.0 g p(tBA-co-APVE) of example 4 dissolved in 30 mLTHF were added under ice cooling drop wise 0.76 g (6.7 mmol) acryloylchloride, whereby immediately a white solid precipitates. The reactionmixture was stirred for further 24 h at room temperature. The solid wasfiltered off and the solvent was evaporated. The crude raw material wasused for hydrolysis without further purification.

FT-IR: ν_(max) [cm⁻¹]=3289, 2976 (—CH₂—), 1722 (ester), 1659 (amide I),1628 (—C═C), 1544 (amide II), 1480, 1448, 1366, 1254, 1143, 844.

Hydrolysis of Ester Moieties to P(AA-co-APVE-AA)

3 g of the modified polymer was added portion wise under stirring to 10mL trifluoro acetic acid, and stirred some hours at room temperatureprior to evaporate the trifluoro acetic acid in vacuum. The obtainedhigh viscous polymer was dissolved in water and adjusted to pH 2 byaddition of aqueous NaOH. Then the solution was dialyzed for 4 days(MWCO=1000 g/mol). After frieze drying a colorless solid was received.

FT-IR: ν_(max) [cm⁻¹]=3361, 2930 (—CH₂—), 1707 (acid), 1654 (amide I),1620 (—C═C), 1544 (amide II), 1447, 1407, 1242, 1179, 1097, 980, 801.

¹H-NMR (300 MHz, D₂O): δ (ppm)=6.3 (1H, —C═C—H), 6.2 (1H, —C═C—H), 5.8(1H, —CH═C<), 3.6 (2H, —O—CH₂—), 3.3 (2H, —NH—CH₂—), 2.2 (1H, backbone),1.9-1.4 (2H, backbone), 1.6 (2H, —O—CH₂—CH₂—).

Example 6 Copolymerisation of Acrylic Acid and N-Vinyl Formamide ¹ toP(AA-NVFA)

3 g (41.6 mmol) acrylic acid and 590 mg (8.9 mmol) N-Vinylformamide weredissolved in 10.88 g distillated isopropanol and aerated with nitrogenfor 30 minutes. Then 164 mg (2 mol-%) AIBN were added in the nitrogencounter flow and aerated with nitrogen for further 15 minutes. Then thesolution was stirred for 24 h at 70° C., whereby a colorless solidprecipitated. The solid was filtered off and washed repeatedly withacetone and dried under reduced vacuum. One obtained a colorless, finedispersed solid. ¹ N. A. Nesterova et alter, Russian Journal of AppliedChemistry 2008, Vol. 82, No. 4, pp. 618-621

FT-IR: ν_(max) [cm⁻¹]=3272 (—NH₂), 3054 (—CH₂—), 2922, 1708 (acid), 1643(amide I), 1532 (amide II), 1444, 1385 (—CH₂—), 1244, 1178.

¹H-NMR (300 MHz, DMSO-d₆): δ (ppm)=12.2 (1H, —COOH), 7.9 (1H, —NH—COH),4.3 (1H, —CH—NH), 2.2 (1H, —CH—COOH), 1.7 (2H, —CH₂—CH—NH—), 1.5 (2H,CH₂—CHCOOH).

GPC (H₂O): M_(n)=10 kDa, M_(w)=49 kDa, M_(z)=126 kDa, PD=5.0.

Conversion of P(AA-co-NVFA) Into P(AA-co-VAm)

(based on the hydrolysis of pure p(VFA) to provide p(VAm), in K.Yamamoto et alter, Journal of Applied Polymer Science 2002, Vol. 89, pp.1277-1283.

200 mg of the copolymer p(AA-co-NVFA) were dissolved in 10 mL 2 N NaOHand stirred for 2 h at 100° C. Then the solution was neutralized by HCland dialyzed for 3 days (MWCO=1000 g/mol). After freeze drying afleece-like colorless solid was obtained.

FT-IR: ν_(max) [cm⁻¹]=3274 (—NH₂), 2919 (—CH2-), 1666 (—COONa), 1559(—NH₂), 1448, 1408 (—CH₂—), 1188 (—C—O—).

¹H-NMR (300 MHz, D₂O): δ (ppm)=2.5 (1H, —CH—NH₂), 2.0 (1H, —CH—COOH),1.4 (2H, —CH₂—CH—NH₂), 1.3 (2H, —CH₂—CH—COOH).

Acrylamide Modified P(AA-co-VAm-MA)

0.5 g of the hydrolyzed copolymer P(AA-co-VAm) were added to a roundbottom flask and an excess of 1.0 g methacrylic anhydride were added.The mixture was heated to 60° C. for 4 hours. Then the product wasdiluted in water and the polymer was precipitated in methanol twice. Thefinal polymer was analyzed for functionalization with double bonds by¹H-NMR (C═C bonds at 5.51 ppm and 5.31 ppm). The polymer is soluble inwater after stirring for 24 hours. The degree of functionalizationreaches 4.0 mol-%.

Example 7 Copolymerisation of Acrylic Acid and N-(2-AminoEthyl)Methacryl Amide Hydrochloride

0.2 g (3 mmol) acrylic acid and 0.5 g (3 mmol) N-(2-aminoethyl)methacryl amide hydrochloride were dissolved in 1.4 g DMF andaerated with nitrogen for 15 minutes. Then 20 mg (2 mol-%) VA-044 wereadded in the nitrogen counter flow and aerated with nitrogen for further5 minutes. Then the solution was stirred for 2 h at 70° C., whereby acolorless solid precipitates. The solid was filtered off and washedrepeatedly with acetone and dried under reduced vacuum. One obtained acolorless, fine dispersed solid.

FT-IR: □_(max) [cm⁻¹]=3350 (—NH₂), 2926, 1705 (acid), 1629 (amide I),1527 (amide II), 1482, 1456, 1393, 1365, 1232, 1166, 837.

¹H-NMR (300 MHz, DMSO-d₆): δ (ppm)=12.3 (1H, —OH), 8.3 (1H, —NH—), 7.9(2H, —NH₂), 4.2 (1H, CH3-CH<), 2.9 (2H, —NH—CH₂—), 2.6 (2H,—NH—CH₂—CH₂—), 1.5 (1H, backbone), 1.2 (3H, —CH₃), 1.0 (2H, backbone).

The invention claimed is:
 1. A polymerizable polymer produced by theprocess comprising: (a) a step of copolymerizing a mixture comprising(i) a first copolymerizable monomer comprising at least one protectedcarboxylic acid group or unprotected carboxylic acid group and a firstpolymerizable organic moiety, and (ii) a second copolymerizable monomercomprising one or more protected or unprotected primary and/or secondaryamino groups and a second polymerizable organic moiety, for obtaining anamino group containing copolymer; b) a step of coupling to the aminogroup containing copolymer a compound having a polymerizable moiety anda functional group reactive with an amino group of repeating unitsderived from the second copolymerizable monomer in the amino groupcontaining copolymer obtained in the first step, wherein the protectedamino group is deprotected, so that polymerizable pendant groups arelinked to the backbone by hydrolysis-stable linking groups, (c) furtherincluding a step of deprotecting any of the protected carboxylic acidgroup after step (a) or step (b), for obtaining the polymerizablepolymer.
 2. The polymerizable polymer according to claim 1, wherein thefirst copolymerizable monomer is represented by the general formula (1):

wherein R¹ is a hydrogen atom, a —COOZ group or a straight chain orbranched C₁₋₆ alkyl group which may be substituted by a —COOZ group; R²is a hydrogen atom, a —COOZ group or a straight-chain or branched C₁₋₆alkyl group which may be substituted by a —COOZ group; A is a singlebond or a straight-chain or branched C₁₋₆ alkylene group which group maycontain 1 to 3 heteroatoms in between two carbon atoms of the alkylenecarbon chain, which heteroatoms are selected from an oxygen atom,nitrogen atom, and sulfur atom, and/or which alkylene group may containin between two carbon atoms of the alkylene carbon chain 1 to 3 groupsselected from an amide bond or a urethane bond; Z which may be the sameor different, independently represents a hydrogen atom, a metal ion, aprotecting group for a carboxylic acid group, or the Z forms with afurther —COOZ group present in the molecule an intramolecular anhydridegroup.
 3. The polymerizable polymer according to claim 1, wherein theprotecting group for a carboxylic acid group of the firstcopolymerizable monomer and second copolymerizable monomer is selectedfrom a trialkylsilyl group, an alkyl group, and an arylalkyl group, orwherein the protecting group for an amino group of the firstcopolymerizable monomer and second copolymerizable monomer is selectedfrom an acyl group, an arylalkyl group, an alkoxy carbonyl group, and anaryloxycarbonyl group.
 4. The polymerizable polymer according to claim1, wherein the first copolymerizable monomer is a protected(meth)acrylic acid monomer.
 5. The polymerizable polymer according toclaim 1, wherein the protecting group for a carboxylic acid is selectedfrom a tert-butyl group and a benzyl group.
 6. The polymerizable polymeraccording to claim 1, wherein the first copolymerizable monomer isselected from tert-butyl acrylate and benzyl acrylate.
 7. Thepolymerizable polymer according to claim 1, wherein the secondcopolymerizable monomer is represented by the general formula (2):

wherein R³ is a hydrogen atom or a straight chain or branched C₁₋₆ alkylgroup which may be substituted by a —COOZ′ group; X is a protected aminogroup or a hydrocarbon group having 1 to 20 carbon atoms, which issubstituted with an amino group which may carry a protecting group,wherein the hydrocarbon group may contain 1 to 6 heteroatoms, whichheteroatoms are selected from an oxygen atom, nitrogen atom, and sulfuratom, and/or which hydrocarbon group may contain a group selected froman amide bond or a urethane bond and which hydrocarbon group may furtherbe substituted with up to 6 groups selected from —COOZ′, amino groups,hydroxyl groups and thiol groups; Y is a hydrogen atom, a —COOZ′ group,or a hydrocarbon group having 1 to 20 carbon atoms, wherein thehydrocarbon group may contain 1 to 6 heteroatoms, which heteroatoms areselected from an oxygen atom, nitrogen atom, and sulfur atom, and/orwhich hydrocarbon group may contain a group selected from an amide bondor a urethane bond and which hydrocarbon group may further besubstituted with up to 6 groups selected from —COOZ′, amino groups,hydroxyl groups and thiol groups; Z′ which may be the same or different,independently represents a hydrogen atom, a metal ion, a protectinggroup for a carboxylic acid group, or the Z′ forms with a further —COOZ′group present in the molecule an intramolecular anhydride group.
 8. Thepolymerizable polymer according to claim 1, wherein the secondpolymerizable organic moiety of the second copolymerizable monomer isselected from the group of (meth)acrylamide moieties which may besubstituted and substituted (meth)acrylic acid which may be protected.9. The polymerizable polymer according to claim 1, wherein the secondcopolymerizable monomer is selected from allyl amine, aminopropyl vinylether, aminoethyl vinyl ether, N-vinyl formamide, and 2-aminomethylacrylic acid.
 10. The polymerizable polymer according to claim 1,wherein the molar ratio of first copolymerizable monomer and secondcopolymerizable monomer in the mixture copolymerized in step (a) (molfirst copolymerizable monomer/mol second copolymerizable monomer) is inthe range of from 100:5 to 5:100.
 11. The polymerizable polymeraccording to claim 1, wherein the compound having a polymerizable moietyand a functional group reactive with an amino group of repeating unitsderived from the second copolymerizable monomer is a compound of formula(3):

wherein R⁴ is a hydrogen atom or a straight chain or branched C₁₋₆ alkylgroup which may be substituted by a —COOZ″ group; R⁵ is a hydrogen atomor a straight-chain or branched C₁₋₆ alkyl group which may besubstituted by a —COOZ″ group; Z″ which may be same or different,independently represents a hydrogen atom, a metal ion, a protectinggroup for a carboxylic acid group, or the Z″ forms with a further —COOZ″group present in the molecule an intramolecular anhydride group; and LGis a leaving group, or wherein LG may replace Z″ and form with R⁴ or R⁵an intramolecular carboxylic acid anhydride group, or wherein twomolecules of formula (3) form an intermolecular carboxylic acidanhydride group by condensation of LG and/or —COOZ″, wherein LG is anoxygen atom.
 12. The polymerizable polymer according to claim 1, whereinthe coupling reaction in step (b) is an addition reaction or acondensation reaction forming a bond selected from an amide bond, a ureabond or a thiourea bond.
 13. A dental composition comprising thepolymerizable polymer produced by the process comprising: (a) a step ofcopolymerizing a mixture comprising (i) a first copolymerizable monomercomprising at least one protected carboxylic acid group or unprotectedcarboxylic acid group and a first polymerizable organic moiety, and (ii)a second copolymerizable monomer comprising one or more protected orunprotected primary and/or secondary amino groups and a secondpolymerizable organic moiety, for obtaining an amino group containingcopolymer; b) a step of coupling to the amino group containing copolymera compound having a polymerizable moiety and a functional group reactivewith an amino group of repeating units derived from the secondcopolymerizable monomer in the amino group containing copolymer obtainedin the first step, wherein the protected amino group is deprotected, sothat polymerizable pendant groups are linked to the backbone byhydrolysis-stable linking groups, (c) further including a step ofdeprotecting any of the protected carboxylic acid group after step (a)or step (b), for obtaining the polymerizable polymer; wherein the dentalcomposition further comprises a filler, an initiator system and one ormore additional comonomers.